1Field of the Invention
The present invention relates generally to management of the internal interconnection of the ports and media access control layers (MACS) within a node of a data transmission network that operates substantially in accordance with the FDDI protocol. More particularly, a hardware based user interface is provided that permits the user to readily control port and MAC interconnections.
2. Discussion of the Prior Art
One type of high speed data transmission network is defined by the Fiber Distributed Data Interface (FDDI) protocol. The FDDI protocol is an American National Standards Institute (ANSI) data transmission standard which applies to a 100 Mbit/second token ring network that utilizes an optical fiber transmission medium. The FDDI protocol is intended as a high performance interconnection between a number of computers as well as between the computers and their associated mass storage subsystem(s) and other peripheral equipment.
Information is transmitted on an FDDI ring in frames that consist of 5-bit characters or "symbols", each symbol representing 4 data bits. Information is typically transmitted in symbol pairs or "bytes". Tokens are used to signify the right to transmit data between stations. The FDDI standard includes a thirty-two member symbol set. Within the set, sixteen symbols are data symbols (each representing 4 bits of ordinary data) and eight are control symbols. The eight control symbols are: J (the first symbol of a start delimiter byte JK), K (the second symbol of a start delimiter byte JK), I (Idle), H (Halt), Q (Quiet), T (End Delimiter), S (Set) and R (Reset). The remaining eight symbols of the FDDI standard symbols set are not used since they violate code run length and DC balance requirements of the protocol. These are referred to as V (violation) symbols. In operation, a continuous stream of control symbol patterns defines a "line state". The FDDI protocol defines several line states that are used during the connection management sequence.
The FDDI Station Management (SMT) standard provides the necessary control of an FDDI station (node) so that the node may work cooperatively as a part of an FDDI network. To effectively implement the functions required, SMT is divided into three entities, namely the Connection Management entity (CMT), the Ring Management entity (RMT) and the Frame Based Services. The Connection Management (CMT) is the management entity in the Station Management that is responsible for the station's port(s), as well as the connection to the ports of neighboring stations.
The Connection Management is further divided into three sub-entities. They include, the Physical Connection Management (PCM), Configuration Management (CFM) and Entity Coordination Management (ECM). A general description of the Station Management standard, as well as each of its subparts, including the Connection Management (CMT), the Configuration Management (CFM) and the Physical Connection Management (PCM) is described in detail in the draft ANSI FDDI Station Management Standard, dated Jun. 25, 1992, which is incorporated herein by reference.
Although the FDDI protocol is based primarily on the concept of a dual ring wherein communications are possible between nodes in both directions (i.e. a duplex connection), some parties have proposed that the FDDI-2 standards facilitate the use of simplex connections as well. Simplex connections are intended to connect single-attachment stations. The intent of the simplex connection scheme is to permit the transmission of ring information through stations on a lobe. Within the lobe, communication would be possible in only one direction. Thus, when the lobe is in operation, all information within the ring would pass directly through each station on the lobe.
Nodes that may be used within an FDDI network generally fall into the classifications of single attachment nodes and dual attachment nodes. Dual attachment nodes have two ports to accommodate the dual trunk rings of the FDDI network. Single attachment stations have a single port and therefore cannot directly attach to the dual trunk rings. Rather, the single attachment stations typically are coupled to the trunk rings through a concentrator that forms the root of a tree. The concentrator may be single attachment or a dual attachment type. Thus, as seen in FIG. 1, a typical FDDI network may consist of a plurality of dual attachment nodes arranged in a trunk ring 210. The dual attachment nodes may include both dual attachment stations 211 and dual attachment concentrators 212. Each dual attachment concentrator 212 forms the root of a concentrator tree 215. As seen in FIG. 1, the concentrator tree may include various single attachment concentrators 217 that form the root of tree branches and single attachment stations 219. As used hereafter, the terms "node" and "station" are intended to be generic and apply to both formal FDDI stations and FDDI concentrators.
Each dual attachment node contains two Ports designated as A and B. Port A is intended to be connected to the primary ring on the incoming fiber and the secondary ring on the outgoing fiber. Similarly, Port B is intended to be connected to the incoming fiber of the secondary ring and the outgoing fiber of the primary ring. Therefore a properly formed trunk ring is composed of a set of stations with the Port A of one station being connected to the port B of the neighboring station.
Concentrator nodes contain one or more Ports of type M to provide connections within a concentrator tree. A single attachment node (whether it be a station or concentrator) has an S type Port which is intended to be attached to an M type port within a concentrator tree. Accordingly, a standard FDDI network would typically have as many as four different types of ports. That is, A, B, M, and S type ports.
The FDDI network topology may be viewed at two distinct levels. That is the physical topology and the logical topology. Physical topology describes the arrangement and interconnection of nodes with physical connections. In contrast, logical topology describes the paths by which tokens and information flow through the network between MACs. The logical and physical topologies of an FDDI network are not necessarily the same. The tree structure provided through concentrators can have the token path entering and exiting the concentrator many times on the same ring, where logically, each concentrator MAC will only appear once on a ring. That is, the token will only pass once through the concentrator's MAC. Also, the number of MACs and attachments in a station need not be equal, so a station in the trunk ring may be physically in both rings, but may be in only one of the logical rings.
Under the normal FDDI standard, all physical connections are duplex links. In a fully connected trunk ring, a duplex link supports counter-rotating rings, whereas in a tree, the duplex link provides transmit and receive paths for one of the dual rings. As seen in FIG. 1, these two connection structures can be combined to produce a dual ring that may include a variety of trees in a fully connected network. The dual ring includes a primary ring and a secondary ring. A concentrator is provided at the base of each tree. Single attachment concentrators transmit information from one of the rings down through their associated tree. The ring chosen to logically extend down a tree may be either the primary or the secondary ring. On the other hand, a dual attachment concentrator has the ability to extend both logical rings down associated trees, thereby forming two separate trees (one with the primary ring and another with the secondary ring).
The introduction of an FDDI station (node) into the data flow path of the FDDI ring is governed by the Physical Connection Management (PCM) entity. To accomplish this, the PCM initializes the connection of neighboring ports and manages the line state signalling. Therefore, the PCM provides all of the necessary signalling to initialize a connection, to withhold a connection on a marginal link and to support maintenance. In order to manage the initial connection between neighboring ports of separate stations, the PCM manages the physical layer, controls the line-states transmitted during initiation and monitors the line-states received during the connection initialization.
The connection process is achieved through a lock-step handshaking procedure. In the basic FDDI sequence, the handshaking procedure controlled by the PCM is divided into three stages. They include an initialization sequence, a signaling sequence and a join sequence. The initialization sequence is used to indicate the beginning of the PCM handshaking process. It forces the neighboring PCM into a known state so that the two PCM state machines can run in a lock-step fashion.
Following the initialization sequence is the signaling sequence. The signaling sequence communicates basic information about the port and the node with the neighboring port. A Link Confidence Test (LCT) is also conducted during the signaling sequence to test the link quality between the two ports. If the link quality is not acceptable or the type of connection is not supported or is currently not accepted by the nodes then the connection will be withheld. If the connection is not withheld during the signaling sequence, the PCM state machine can move on to the join sequence and establish a connection between the two neighboring ports.
The PCM is responsible for sending two signals to the Configuration Management (CFM) state machine. They are the CF.sub.-- Join flag and the CF.sub.-- Loop flag. The CF.sub.-- Join flag is activated at the end of the join sequence when the node is to be inserted into the active transmission ring. Thus, it signals the CFM to establish an active connection. The CF.sub.-- Loop flag is intended to provide a path to the neighboring port for extended link testing or information exchange prior to the establishment of an active connection. Thus, the CF.sub.-- Loop flag is activated when the PCM desires to execute a loop test during the signalling sequence portion of the connection management sequence.
The Configuration management (CFM) is responsible for defining the interconnections of the ports and MAC(s) within a node. Thus, the CFM controls the routing of data within the node. In hardware implementations, the routing is controlled by programming a configuration switch based on the CFM control flags issued by PCM and on the overall node path configuration. The FDDI SMT standard contemplates that there are numerous internal configurations that an FDDI node must be able to support. For example, any given port may be in an isolated path configuration. In this situation, data received through an input line P.sub.in would be passed directly out of the port through the output line P.sub.out of the same port.
The usual active FDDI configuration for a dual attachment station on a trunk ring is a "thru path" arrangement wherein the network's primary data transmission path enters the A port, passes through the nodes internal primary path and emerges from the B port. At the same time the network's secondary data transmission path enters the B port, passes through the nodes internal secondary path and exits through the A port. The internal paths may require the data to physically pass through one or more MACs. Alternatively, the port may be connected in a concatenated path arrangement wherein after entering through the input line P.sub.in of a particular port, the data path passes through both the primary and secondary internal data paths within the node before exiting the output line P.sub.out of the same port. In a dual attachment station, this arrangement is particularly likely in the event of a failure in the connection between one of the local ports and its remote neighbor. The internal configurations that are permissible in accordance with the FDDI standards are set forth in detail in the above referenced SMT standard. However, it is important to note that system designers (users) may wish to implement other (non-standard) internal path configurations as well in order to facilitate a particular design requirement. Thus, it is important that the user be provided with a mechanism for implementing a wide variety of internal node path configurations.
FDDI nodes will often include two or more MACs. Typically, each MAC would appear logically at only one point in the ring. Thus, a MAC is typically a logical member of just one of the primary, secondary and local (if any) rings. The Configuration Management permits the ports to be attached to these MACs in a variety of manners. By way of example, in a dual attachment node that forms a part of the trunk ring, a main MAC might be used in the primary ring during active transmission, while the secondary MAC is used in the secondary (or backup) ring. However, in such a system, it may be desirable to use the secondary MAC to conduct the loop tests during the connection process of any port. Therefore, the Configuration Management must permit reconfiguration of the ports and MACs during the connection initiation procedures.
In another example, in the event of a failure in the primary MAC, it may be desirable to insert the second MAC into the primary ring and eliminate it from the secondary ring. Of course a wide variety of other configurations are contemplated by the FDDI station management standard as well. In other specific applications, system designers (users) may wish to provide different port to MAC configurations to suit a particular need. Indeed, in some systems it may be desirable to utilize both the primary and secondary rings for data transmission to increase the system's throughput. Therefore, it is desirable to provide a physical layer controller that permits the user to easily control the port and MAC configurations regardless of the number of ports and MACs that are provided. In order to facilitate high speed connections, it is also desirable to provide a physical layer controller that can accomplish the connection management functions with minimal software intervention.